The ongoing investigation into a door plug that blew out mid-flight on an Alaska Airlines flight is continuing to impact travelers, with both Alaska and United Airlines cancelling hundreds of flights due to the grounding of their fleets of Boeing 737 Max 9 jets.

The airlines are the only two U.S. passenger airlines that operate flights on the Boeing 737 Max 9 aircraft, the jet involved in the mid-air blowout. In the aftermath of the incident, both airlines say they have found loose hardware on door plugs on several Boeing 737 Max 9 planes.

The Federal Aviation Administration said all Boeing 737 Max 9 planes in the U.S. will be grounded until the agency is "satisfied that they are safe," an agency spokesperson said in a statement Sunday.

While passengers may feel relief they won't be booked on Boeing 737 Max 9 flights for the time being, the incident and subsequent investigation are causing major disruptions to Alaska and United's flight schedules. 

How many flights are cancelled or delayed?

More than 200, or 8%, of United departures were cancelled as of Tuesday morning. Another 171, or 7%, of flights were delayed, according to flight tracking site FlightAware. 

Alaska Airlines cancelled 108, or 18%, of its scheduled flights Tuesday. Another 45 flights were delayed, representing 7% of the airline's scheduled departures. 

Cancellations on the two airlines combined made up nearly half of all U.S. flight cancellations Tuesday. 

What can I do if my flight is cancelled?

Alaska Airlines customers whose flights are affected by the investigation have a number of options, Alaska said in a statement on X, formerly known as Twitter. 

The airline has implemented a "flexible travel policy" that allows passengers whose flights were changed or cancelled to rebook or seek refunds. They can rebook their flights, earn flight credit for future use or request a refund. It doesn't matter when they purchased their tickets. 

The airline is also allowing guests scheduled to travel on Boeing 737 Max 9 planes through January 20 to request alternate accommodations. If the airline can not find a suitable alternative, customers are entitled to full refunds, the airline said on its website. 

Meanwhile, United customers are permitted to reschedule their trips at no additional cost, with the airline waiving any usual change fees or fare differences, United said on its website. The new flight must be scheduled to depart on or before January 18.

Passengers may also request full refunds of flights booked on Boeing 737 Max 9 aircraft under United's policy. 

What are my legal rights?

Generally speaking, whenever an airline in the U.S. cancels a flight, passengers are owed refunds if they choose not to rebook their flights or travel for whatever reason. This applies equally to all fare types, including non-refundable fares. Customer refunds are also due in the event of "significant" delays or flight schedule changes. 

However, the law is deliberately ambiguous and allows airlines to define what constitutes an eligible delay. 

Under Alaska's policies, flights that are delayed by at least one hour are considered significantly delayed, which travel expert Scott Keyes said is among the best policies in the U.S.

"Most airlines say it's two or three hours, so that's a big thing to be aware of," he said. 

In:
• Alaska Airlines
• United Airlines

Megan Cerullo

Megan Cerullo is a New York-based reporter for CBS MoneyWatch covering small business, workplace, health care, consumer spending and personal finance topics. She regularly appears on CBS News streaming to discuss her reporting.